1. Field of the Invention
The invention relates to a lawn tractor which includes a worm type mower housing and a mower mechanism arranged between the four traction wheels, the rotary mower blade thereof being provided with air vanes or the like formed thereon for conveyance of grass clippings, a discharge conduit extending upwardly to a rear mounted detachable grass catcher bag, and a grass catcher hood pivotally mounted on a horizontal swivel shaft to cover the top of the bag in its horizontal swivel position.
2. Background of the Invention
Since the undercarriage necessarily provided on fourwheel lawn tractors requires the mower mechanism and the rear mounted grass catcher bag to be spaced relatively far apart, the discharge conduit of the mower housing is designed to form an enclosed conduit behind its spiral section in order to permit optimum utilization of the blowing capacity of the rotary air-vane type mower blade for conveyance of the grass clippings. However, an enclosed discharge conduit is very likely to become plugged especially when grass clippings are not completely dry and, very often, the catcher bag will not receive the full fill as would be desirable for the economical operation of a lawn tractor.
As prior art, German patent reference No. DE 34 06 606 A1 should first be mentioned, although it is less concerned with the grass clipping conveyance problem. The dynamics of grass clipping conveyance are more fully discussed in U.S. Pat. Nos. 4,532,755 and 4,106,272 which describe measures for preventing generation of back pressure in the discharge conduit, which may cause plugging thereof. Basically, these measures consist in giving the grass conveying air a chance to escape into the open after the airstream enters underneath the cover or grass catcher hood without letting the grass escape along with the air. Thus, it is known to provide the cover with a screen-like outlet at a suitable point somewhere aside from the path of the forced airstream so as to prevent escapement of the grass clippings, yet permitting air discharge. The simplest method of discharging air without simultaneous discharge of grass clipping consists in the use of a permeable catcher bag (European patent reference No. EP 72 572 A1), corresponding to U.S. Pat. No. 4,393,645. This method, however, requires the bag to be made of textile fabric, a costly material, and is thus unsuitable for throw-away bags. German patent reference No. DE 25 37 120 A1, corresponding to U.S. Pat. No. 3,958,401, therefore recommends insertion of an impermeable collecting bag of synthetic material into an external permeable bag to create an expansion zone for inflowing air underneath the cover. Grass clippings are conducted into the internal collecting bag, whereas the air is permitted to escape through the space present between the two interfitted bags and through the external permeable bag. In this case, the internal collecting bag may be of throw-away bag construction.
The difficulties inherent in grass clipping conveyance is particularly evident on lawn tractors featuring grass discharge from the side of the mower housing and, accordingly, with a discharge conduit extending laterally upwardly as disclosed in U.S. Pat. No. 4,532,755, European patent reference No. EP 72 572 A1 and German patent reference No. DE 25 37 120 A1, as far as the latter actually describes an automotive lawn tractor.